Preparation of dl-menthone



Patented Feb. 22, 1949 PREPARATION OF DL-MENTHONE Arthur L. Barney, West Lafayette. Ind., assignor to Purdue Research Foundation, La Fayette, Ind, a corporation of Indiana Y No Drawing. Application August 18, 1942,

Serial No. 455,219

This invention is concerned with the preparation of dl-menthone and is particularly directed to a process for the isolation of dl-menthone by rectification from mixtures initially comprising substantial quantities of isomers and precursors thereof.

The synthesis of menthol from isopropyl methyl phenol has been accomplished by hydrogenation of thymol (Z-isopropyl-5-methylphenol) subsequent separation of dl-menthone from the resultant mixed reaction product, and reduction of the menthone to form menthol. This process has been described and claimed in my co-pending application Serial 441,466 filed May 2, 1942, now abandoned, of which the present application is a continuation-in-part.

One disadvantage accruing to the above process is the relatively low yield of dl-menthone normally obtainable from the hydrogenation of thymol. The crude reaction product obtained by such hydrogenation is a complex mixture of ketonic and alcoholic products from which dlmenthone should be isolated in substantially pure form prior to subsequent reduction if a dl-menthol product of reasonable purity'is to be obtained. While the foregoing process is operable as far as the preparation and separation of the dl-menthone formed during the hydrogenation is concerned, improved procedures whereby a higher percentage of dl-menthone may be formed and separated are to be desired.

It is an object of the present invention to provide a process for the recovery of dl-menthone in high yields from the hydrogenation products of thymol. It is a further object to provide means whereby ketonic and alcoholic products embodying hexahydro-isopropyl-methyl-phenyl structures may be so modified as to permit the recovery therefrom of dl-menthone in high yield. Another object of the invention is to provide a method whereby a higher over-all yield of dlmenthol can be obtained from dl-menthone. Other objects of the invention will become apparent from the following specification.

I have discovered that when alcoholic and ketonic mixtures comprising hexahydro-thymol and the corresponding ketones (similar to those obtained by the hydrogenation of thymol) are rectified in the presence of copper chromite, Raney nickel catalyst, with or without additional alkali metal base, a rearrangement or combined rearrangement and dehydrogenation takes place whereby all or essentially all of such alcoholic and ketonic products become transformed to dlmenthone and are recoverable as such.

2 Claims. (01. 260-587) As raw materials in this process, any mixed product of the reduction of thymol products such as hydrogenated piperitone regardless of method of preparation, may be employed. If preferred, any dl-menthone initially present in such mixture may be stripped off and the residues employed in the present process. A further raw material consists of essentially alcohol-free ketone mixtures rich in menthones, and isomenthones. An additional source of raw material resides in the impure fore-fractions and residues from the distillation of synthetic dl-menthol as described in my co-pending application as above-identified. Likewise substantially pure isomenthone may be employed. It is to be understood that the present invention is not limited in any Way to the use of products obtained by the hydrogenation of thymol. While the latter constitutes a preferred embodiment of the invention, similar products, regardless of the manner in which they are prepared, may be substituted therefor.

In operating in accordance with my new process, a certain amount of discretion may be exercised in the choice of the catalyst employed. For the treatment of'compositions consisting essentially of alcohols or of ketone-alcohol mixtures comprising an appreciable proportion of the alcoholic constituent, a mixture of the copper chromite catalyst "and alkali metal base is preferably employed. Where the raw material to be treated consists essentially of ketones, the alkali metal base alone may be sufiicient. In the event Raney nickel is employed, the small amount of alkali present therein permits of its use alone provided suificient quantities thereof are employed.

The procedure may be carried out at any suitable temperature and with any suitable proportion of catalyst. The operable range appears to be at a pot temperature of between about the boiling temperature of dl-menthone at the pressure employed and the temperatureat which decomposition of the reaction mixture takes place, and generally not to exceed about 200C. The preferred temperature to a considerable degree determined by the nature of the alcohol, ketone, or alcohol-ketone mixture employed, the proportion of catalyst included in the mixture to be rectified, the reflux ratio of the rectification tower, and the efiiciency of the tower. Similarly, the proportion of catalyst required; is a functoin of the forego ing elements plus the temperature of operation. From about 1 to about 10 per cent of the Raney nickel or copper chromite catalyst and/or from about 0.1 to l per cent'or higher, of sodium'hy droxide, all based upon the weight of the rectification mixture, may be employed. The preferred reflux ratio at which rectification is carried out is similarly dependent upon the efiiciency of the rectification column, the nature of the product under treatment, the nature and proportion of catalyst, and the temperature of operation.

In carrying out the reaction the catalyst and ketonic or alcoholic product are mixed together in the pot of the rectification apparatus and heated to the desired temperature under reduced pressure. The dl-ment-hone is recovered as a lower-boiling Higher-boiling fractions or residues may be reutilized in the process. 7

The following examples illustrate the invention but are not to be construed as limiting the same.

Example 1 One hundred thirty three milliliters of a mixed ketonic product consisting predominately of (11-- isomenthone but containing F small amounts ,of isomeric menthol's, 0.1 gram of sodium hydroxide, and; grams of Raney nickel catalyst were mixed together and rectified in a 60 plate column under reduced pressure. A small portion of the reaction mixture was lost due to a small leak developing in the apparatus. The remainder of the charge was rectified at a high reflux ratio to obtaina substantially c uantit'ative yield of pure d-1 menthone boiling at 7577 Cu at 20 millimeters pressure and forming a scmicarbazone melting at led-158 C. A semicarbazone preparation of the original material melted at from 147to 194? C. The residue from the distillation amounted to less than grams.

Example 2 fraction from the rectification.

one hundred forty three g-ra-rnsof hexahydro thymcl, 10 grams of Raney nickel catalyst, and 0.5 gram of sodium hydoxide were mixed together and rectified under reduced pressure at a'bath temperature of 1d0150 'C. and under high re flux ratio through a 60-plate column. The recovery of dl-menthone amounted to substantially 100 per cent of theoretical. To obtain this result, it was found necessary to add small additional amounts of Barley nickel catalyst from time to time during the rectification operation. The residue from this operation consisted essentially of nickel and sodium hydroxide.

Example 3 One hundred ninety two milliliters or crude hydrogenated thyrhol (containing both alcoholic and ketonio products and 10-15 per cent of petroleum ether), and 10 grams of Rany nickel catalyst were inixed together and rectified under reduced pressure through a 60 plate column substantially as described in the preceding example. 7

As a product from this rectification, there was obtained 25 milliliters of petroleum ether'and 3.08 milliliters of dl-menthon. A' higher boiling fraction consisted of 14 milliliters of a mixture of dl-menthone and thymol. The latter was apparently carried over unrcacted in the crude hydrogenation product or was produced by dehydrogenation of menthone and/or isomenthone."

The residue from the operation consisted of 5 grams of thymol and 10 grams of nickel.

Example 4 A mixture obtained r n n chromiclacid oxidation of hexahydrothymol and comprising approximately 90 per cent ketonic products was 4 mixed with 1 per cent'by weight of solid sodium hydroxide. This mixture was charged into a distillation pot and rectified under reduced pressure and high reflux ratio through a 9-foot glass tower packed with inch Raschig rings and having an efiiciency of 15-20 plates. The product from this reaction corresponded 'closelyin characteristic to pure dl-m'nthone.

Example 5 The procedure of Example 2 was repeated, 8 grains of copper chromite catalyst being substituted for the Raney nickel. The results obtained were substantially the same as those of Example 2, except that it was unnecessary to supply additional quantities of catalyst during the rectification operation.

As described in said co-pending application, dlmerithoii'e may be reduced with finely divided sodium and an other such as dibutyl ether or a heavy mineral oil; or with calcium and a dialkyl ether; or with hydrogen and nickel in methyl alcohol or other solvents or. by other procedures;

This procedure yields dl-neomenthol concurrently'with dl menthol. Such dl-neomenthol may be recycled in theprocess hereinbefore described source, may be substituted therefore to produce the desired 'dl-menthone. Similarly, in place of sodium hydroxide, potassium hydroxide or other base may beemployed. The catalyst employed in combination with the dehydrogenation catalyst .may be definedas a substance capable of 'pio' moting the attainment of equilibrium in keto enol systems. Thus, the described procedure may be carried out with any alcohol or ketone product embodying hexahydro-isopropyl-methyl+phenyl radicals in which the oxygen atom and at least one of the alkyl groups are on adjacent carbon atoms in the presence of the dehydrogenation,

isomerization, cr dehydrc'genation-isomerization.

catalysts as herein described. a

1 claim: 1. The method which includes: heating a material selected from the group consisting of menthols and menthones other than dl-mentho'ne,

at its boiling point underthepressure employed, with a catalyst selected from the group consisting of Raney nickel and copper chromite, and in the presence ran alkali metal base; and, con-:

densing the dl-menthone Vapors produced.

The process as claimed in claim 1;, wherein the starting material treated is a mixture of menthol and menthone materials.

' ARTHUR i. 7

V REFERENCESCITEED The wi'figifei'erences are of record inth file of this patent: v V UNITED STATES PATENTS Name Date Wotherspoon Jan. 5, 1932i OTHER R F RENCES Number 1939, pdges230-31. V 7

Richters Qrganic Chemistry, Taylor eti-I J 

